Hydraulic mounts, also referred to as hydraulic bearings, are known from the prior art. They serve for the elastic support of assemblies, in particular of motor vehicle engines. Such hydraulic bearings arranged for example between an engine and a chassis of a motor vehicle are intended to be used to prevent engine vibrations from being transmitted to the vehicle chassis. Here, consideration should be given to the known conflict in the field of vibration isolation, which consists in the fact that the bearing should firstly be as rigid as possible in order to be able to accommodate high loads or bearing forces, and secondly must have a soft characteristic in order to isolate to the greatest possible extent vibrations that arise over as broad a frequency range as possible.
In their basic version, such hydraulic bearings normally have a rubber element as a load-bearing spring. The rubber element is often in the form of a hollow cone. The load-bearing spring can thus form a casing wall of the work chamber. On the upper end side of the load-bearing spring, it is possible for a connection element for fastening, in particular the engine, to be attached. The connection element is normally a threaded bolt which can be screwed to the engine. On its underside, the load-bearing spring can be coupled to the main housing in order to allow force transmission from the load-bearing spring to the main housing. The main housing can have fastening elements, in particular radially on the outside. These can serve to fasten the main housing to the vehicle chassis.
When the hydraulic bearing is subjected to a load, a force acts on the load-bearing spring in the longitudinal direction of the hydraulic bearing, such that the load-bearing spring elastically deforms. The deformation is also referred to as compression of the load-bearing spring. In this context, consideration should be given to the fact that the work chamber is at least partially enclosed or surrounded by the load-bearing spring. Thus, the work chamber is reduced in size by the compression of the load-bearing spring, with the result that the pressure in the work chamber increases. If the work chamber is now reduced in size by the compression of the load-bearing spring, the pressure in the work chamber increases, such that a part of the hydraulic fluid flows out of the work chamber, through the throttle duct, and into the equalization chamber. The throttle duct represents a flow resistance for the flowing hydraulic fluid, resulting in a damping action.
The damping characteristics of such hydraulic bearings are frequency-dependent on account of their configuration. Static or quasi-static loads below a frequency of 5 Hz are in this case normally accommodated by the load-bearing spring, which exhibits relatively high stiffness.
Low-frequency vibrations, that is, vibrations with frequencies of approximately 5 to 20 Hz, which generally occur with large amplitudes, are damped by the interaction of the two hydraulic chambers via the throttle duct. Here, the damping arises with the flow of at least a part of the hydraulic fluid from the work chamber, through the throttle duct, into the equalization chamber and vice versa.
High-frequency vibrations, that is, vibrations in the frequency range above 20 Hz up to for example 50 Hz, 100 Hz or 200 Hz, are often transmitted with only very little damping, or even virtually without damping, on account of the inertia, viscosity and incompressibility of the hydraulic fluid and/or the high stiffness and inertia of the load-bearing spring. Although the vibrations generally only occur with small amplitudes, they are of relatively high importance owing to their acoustic action.
With regard to the improved isolation of such vibrations, use is made of what are known as actively controlled hydraulic bearings which each have an actuator, in particular an electric linear actuator. Electromagnetic linear actuators which each have a stator and an armature have proven to be particularly expedient. Here, the armature is configured so as to be mounted in a movable manner with respect to the stator, such that the armature can be deflected relative to the stator in a longitudinal direction of the linear actuator. For the hydraulic bearing, the armature is mechanically connected or coupled to a control diaphragm, which is preferably assigned to an end-side wall of the work chamber, in order to form at least a part of a wall for the work chamber. The control diaphragm can be configured to be elastically deformable in its normal direction. By virtue of the armature being mechanically coupled to the control diaphragm, it is possible for the control diaphragm to be deformed in a controlled manner in its normal direction by way of the electromagnetic linear actuator. Here, provision may be made for the armature not to be connected directly to the control diaphragm, but rather for a joint mechanism and/or an armature plunger, for example, to be provided which are arranged between the armature and the control diaphragm in order to transmit movements and/or forces from the armature to the control diaphragm. The joint mechanism and/or the armature plunger are thus intended to be assigned to the armature. With the deformation of the control diaphragm in its normal direction, the hydraulic volume of the work chamber changes, since the control diaphragm forms preferably a wall part with respect to the work chamber. The actuator of the hydraulic bearing thus also serves to control or change the work chamber volume of the work chamber. By actuation of the actuator and the corresponding action on the control diaphragm, a lowering of the dynamic spring rate of the hydraulic bearing in the range of the high-frequency vibrations can be brought about.
In known hydraulic bearings, the equalization chamber is arranged beneath the work chamber, wherein the work chamber and the equalization chamber are separated from one another by a partition. The partition can be formed partially by the control diaphragm. Such a configuration is known for example from the document WO 2013/127574 A1.
In practice, it has been found that increasingly stringent demands are being made of the available vertical installation space for the active hydraulic bearing. Therefore, there is a need to provide a hydraulic bearing which is configured in a more compact manner in the axial direction.